My '99 C-280 gets 23mpg mixed driving in the summer but when the temperature drops, I get between 19-20. Is this normal?

 

All my cars do it!

 

My fuel mileage drops some in the winter, but usually about only about 1 to 1 1/2 MPG

 

Surprising the extent of the difference?

 

My '00 ML averages about 21 mpg in the summer, and is down to about 17-18 mpg right now. We do have extreme temperataure fluctuationsduring the Fall/Wintermonths. I was wondering the same thing, and am glad to see that someone else has the same problem.

 

Is that in response to the difference I'm experiencing-3 mpg?

BTW, I recently cleaned my MAF- with CRC's MAF sensor cleaner- and worried I'd damaged it; subsequently left with poor mpg.

Fuel price check: I'm paying $2.66/gal.for premium, 91octane, in the Seattle area. What are you paying?

 

JFI.

Fuel got up to 8 USD/ Gallon (US) here in the UK about two months ago. (US gallon is only 80% of a UK gallon!

IF you needed to clean your MAF (mustn't soak it) it would have been due to the CEL coming on which is usually associated with the engine running LEAN (misfire). IF all is now OK your gas mileage/gallon should have worsened SLIGHTLY.

I suspect that the method you use for determining MPG is insufficiently accurate to pick up differences.

Only way you get any meaningful results is BRIMMED tank to BRIMMED tank over an intermediate distance of say 200 miles.

Traffic conditions, weather and style of driving need to be recorded. Short journeys use a LOT more fuel than steady state highway driving (like 100%)

If the ambient is down the air is more dense therefore more fuel is added to give the correct mixture BUT if you drive at the same speed acceleration you should be using less accelerator etc. MPG difference in the normal temp range 0 to 30 C should hardly be noticeable. I suspect that when the car wants to perform well (in cold weather) you take advantage of the situation. My two pennyworth anyway.

IF you have the AirCon on (i.e. the little red LED ib NOT ON this will reduce (make worse) your gas mileage by up to 10% if you are on the highway and a reserved drived.

Stuart

 

Some would contend that MAF performance deteriorates over time well before a CEL comes on. This is due to debris from air filter fibers, dust and pollen, and even oil. This dirt build up on the sensor causes inaccurate measurements; diminishing engine efficiency-again, well before a CEL comes on. It is true that the MAF has a cleaning cycle where the platinum sensor is heated to 1000 deg. F in an attempt to keep the sensor clean. However, this may tend to bake the residue on to the sensor rather than clean it.
Proper maintenance, then, is to clean the sensor at ever air filter change.
I've read of many concoctions and procedures to clean the sensor, however the sensor is a delicate electronic apparatus, housed in plastic. Harsh chemicals such as brake or carb cleaner, can ruin the MAF. I use a product by CRC specifically designed for the job.

My Mercedes uses a hot wire sensor type MAF, which responds directly to air density; meaning ambient temperature is not an issue.

I agree completely.

Thanks for your thoughts.

 

I agree that the MAF characteristics change BEFORE the CEL comes on. However you wouldn't know the extent of the change until the light came on or alternatively accessed the sensor readouts via OBD since the deterioration is due to factors other than straight Time / Mileage of the MAF. Its much more complex. City driving "soot" is a key input to the equation. For some reason this or oil blow by gets past the air filter.

Although there are many proprietary cleaners I have found greatest success with Toluene. Some cleaners do not work. I would NEVER recommend agents like Brake fluid!

Cleaning is NOT recommended by either Mercedes or Bosch however they recognise that on occasions it can work but the longevity of the fix is not able to be Quality assurred so they (not surprisingly) recommend a new EXPENSIVE MAF.

MAF's since about 1996 have been hot film rather than hot wire. Hot wire had a cleaning cycle and gave no trouble other than a broken wire sensors from severe road bumps (vertical). The hot film does not use a cleaning cycle due to the different technology / construction but is much more robust against road inputs.

I said don't soak since the "cleaning agent" causes the seal to the electronics box on the sensor (you refer to it as the plastic casing) to swell with dire results.

Airflow is measured by the change of resistance of the hot wire/film. The greater the flow the lower the temp of the wire which in turn is linked to a change in resistance. Ambient is not an issue but it is a key input into the fuelling map. The colder the air the richer the mixture needs to be.

Is your C280 a M112 V6? If so it uses a hot film sensor unless I am mistaken. The thing on the sensor that looks like a ":hot" wire is in fact the ambient temperature sensor.

Sorry if I disagree with some of your comments but I think you will find my information correct. However I am human should you find an anomaly!

Stuart.

 

Thanks, I didn't know that. I think you have it right.

Damn, I did soak it! I didn't actually remove the sensor from the housing. I didn't have the special torx security bit and couldn't find one to buy, and thinking the temp. sensor was what needed cleaning, I doused it over and over again.

Do you think I should find a torx security bit and do the job right this time; perhaps removeing the seal and lubricating it?